The present invention relates to a hybrid monoclonal antibody. More specifically, the present invention relates to a hybrid monoclonal antibody (hereinafter also simply referred to as hybrid MoAb) having specificities against fibrin and thrombolytic substance and a polydoma which produces said antibody.
The present invention also relates to a thrombolytic agent comprising the above hybrid MoAb and a thrombolytic substance which is immunologically coupled thereto.
Thrombolytic therapy has long been used to treat thrombotic diseases such as myocardial infarction, arterial embolism and cerebral infarction; initially, streptokinase (hereinafter also abbreviated SK), urokinase (hereinafter also abbreviated UK) etc. were clinically applied as efficient thrombolytic agents. Particularly, UK has been relatively commonly used since its fibrinolytic action is strong; however, it is faulty in that its selectivity for fibrin is low and that it acts on fibrinogen as well, and thus it causes a tendency toward bleeding in subject patients. In view of this drawback, tissue plasminogen activator (hereinafter also abbreviated TPA) and prourokinase (hereinafter also abbreviated ProUK) became used as second generation thrombolytic agents. With higher selectivity for fibrin in comparison with UK, these agents were expected to mitigate the adverse effect, i.e., a tendency toward bleeding, of UK; many investigations have so far been made. In recent years, there have been an increasing number of attempts to apply these agents in clinical situations since their massproduction has become possible by use of gene recombination technology [European Cooperative Study Group for Recombinant Tissue-type Plasminogen Activator: The Lancet, 842 (1985)].
These attempts at clinical application, however, revealed that TPA etc. also have some drawbacks; for example, 1 TPA has a very short half life (2 to 3 minutes), thus requiring large-amount long-term administration for thrombolysis, and 2 such high-dose therapy does not always provide a mitigating effect on the tendency toward bleeding.
Under these conditions, more effective thrombolytic agents were investigated and developed; modified TPA, UK-TPA or ProUK-TPA hybrid protein etc. have been produced. As to modified TPA, a TPA mutein lacking part of the sugar chain structure, which is considered a cause of the decrease in half life, has been prepared by gene engineering so that the capture of TPA by sugar-chain receptors of hepatocytes is avoided to improve TPA kinetics in blood. As to UK-TPA hybrid protein, the strong thrombolytic action of UK and the fibrin affinity of TPA are utilized in combination to reduce the administration amount. Although these thrombolytic agents are expected to slightly mitigate the tendency toward bleeding in comparison with conventional thrombolytic agents, significant improvement remains to be achieved by further research and development.
Later, protein complexes based on antibody targeting appeared as third generation thrombolytic agents. That is, thrombolytic agents which lyse fibrin alone without lysing fibrinogen were developed by chemically binding an antibody which does not substantially react on fibrinogen and which possesses high affinity with fibrin alone to UK [C. Bode et al.:. Science, 229, 765 (1985)] or TPA [M. S. Runge et al.: Proceedings of the National Academy of Science, USA, 84, 7659 (1987)]. These antibody-targeting thrombolytic agents are all reported to have exhibited an effect 3 to 100 times stronger than that of simple UK or TPA in experiments in vitro or in vivo. These protein complexes, however, all have drawbacks due to the chemical binding of an antibody and a thrombolytic enzyme; for example, 1 the antibody activity and enzyme activity decrease during the chemical binding procedure, 2 it is difficult to obtain a protein complex of antibody and enzyme in a ratio of 1 to 1, or 3 protein denaturation accelerates the agent's metabolism in the subject patient's body.